It is known in the art to shape a light beam. This has typically been done using an element known as a gobo. A gobo element is usually embodied as either a shutter or an etched mask. The gobo shapes the light beam like a stencil in the projected light.
Gobos are simple on/off devices: they allow part of the light beam to pass, and block other parts to prevent those other parts from passing. Hence mechanical gobos are very simple devices. Modern laser-etched gobos go a step further by providing a gray scale effect.
Typically multiple different gobo shapes are obtained by placing the gobos are placed into a cassette or the like which is rotated to select between the different gobos. The gobos themselves can also be rotated within the cassette, using the techniques, for example, described in U.S. Pat. Nos. 5,113,332 and 4,891,738.
All of these techniques, have the drawback that only a limited number of gobo shapes can be provided. These gobo shapes must be defined in advance. There is no capability to provide any kind of gray scale in the system. The resolution of the system is also limited by the resolution of the machining. This system allows no way to switch gradually between different gobo shapes. In addition, moving between one gobo and another is limited by the maximum possible mechanical motion speed of the gobo-moving element.
Various patents and literature have suggested using a liquid crystal as a gobo. For example, U.S. Pat. No. 5,282,121 describes such a liquid crystal device. Our own pending patent application also so suggests. However, no practical liquid crystal element of this type has ever been developed. The extremely high temperatures caused by blocking some of this high intensity beam produce enormous amounts of heat. The projection gate sometimes must block beams with intensities in excess of 10,000 lumens and sometimes as high as 2000 watts. The above-discussed patent applications discuss various techniques of heat handling. However, because the light energy is passed through a liquid crystal array, some of the energy must inevitably be stored by the liquid crystal. Liquid crystal is not inherently capable of storing such heat, and the phases of the liquid crystal, in practice, may be destabilized by such heat. The amount of cooling required, therefore, has made this an impractical task. Research continues on how to accomplish this task more practically.
It is an object of the present invention to obviate this problem by providing a digital light beam shape altering device, e.g. a gobo, which operates completely differently than any previous device. Specifically, this device embodies the inventor's understanding that many of the heat problems in such a system are obviated if the light beam shape altering device would selectively deflect, instead of blocking, the undesired light.
The preferred mode of the present invention uses a digitally-controlled micromirror semiconductor device. However, any selectively-controllable multiple-reflecting element could be used for this purpose. These special optics are used to create the desired image using an array of small-sized mirrors which are movably positioned. The micromirrors are arranged in an array that will define the eventual image. The resolution of the image is limited by the size of the micromirrors: here 17 .mu.m on a side.
The mirrors are movable between a first position in which the light is directed onto the field of a projection lens system, or a second position in which the light is deflected away from the projection lens system. The light deflected away from the lens will appear as a dark point in the resulting image on the illuminated object. The heat problem is minimized according to the present invention since the micromirrors reflect the unwanted light rather than absorbing it. The absorbed heat is caused by the quantum imperfections of the mirror and any gaps between the mirrors.
A digital micromirror integrated circuit is currently manufactured by Texas Instruments Inc., Dallas, Tx., and is described in "an overview of Texas Instrument digital micromirror device (DMD) and its application to projection displays". This application note describes using a digital micromirror device in a television system. Red, green and blue as well as intensity grey scales are obtained in this system by modulating the micromirror device at very high rates of speed. The inventor recognized that this would operate perfectly to accomplish his objectives.
It is hence an object of the present invention to adapt such a device which has small-sized movable, digitally controllable mirrors which have positions that can be changed relative to one another, to use as a light beam shape altering device in this stage lighting system.
It is another object of the present invention to use such a system for previously unheard-of applications. These applications include active simulation of hard or soft beam edges on the gobo. It is yet another application of the present invention to allow gobo cross-fading using time control, special effects and morphing.
It is yet another object of the present invention to form a stroboscopic effect with variable speed and intensity in a stage lighting system. This includes simulation of a flower strobe.
Yet another object of the present invention is to provide a multiple colored gobo system which can have split colors and rotating colors.
It is yet another object of the present invention to carry out gobo rotation in software, and to allow absolute position and velocity control of the gobo rotation using a time slicing technique.
Another objective is to allow concentric-shaped images and unsupported images.
It is yet another object of the invention to provide a control system for the micromirror devices which allows such operation.
Yet another particularly preferred system is a shadowless follow spot, which forms an illuminating beam which is roughly of the same shape as the performer, and more preferably precisely the same as the performer. The beam shape of the beam spot also tracks the performer's current outline. The spot light follows the performer as it lights the performer. This action could be performed manually by an operator or via an automated tracking system, such as Wybron's autopilot.
Since the beam does not overlap the performer's body outline, it does not cast a shadow of the performer.